Advice for a First Time Solo Traveler on a Budget

Hello Japan Travel, I'm looking for your insight into planning my trip to Japan. I'm going to be there for almost 5 weeks from June to July and it's my first time outside of the US on my own. My budget is really slim, so I'm just going to plan on roughing it for those few weeks. My budget will be around $50/day, so any advice on how to keep things economical is much appreciated. What I would like most is to see the beautiful countryside and the more rural areas of Japan.

Food

Of my budget this will be between $15-$20/day

Transportation

I've decided to skip the JR Pass and do the Willer Express Bus instead, which will save me money from needing accommodations for the night. Your thoughts? Other economical forms of travel?

Lodging

I'm thinking of doing a mixture of couchsurfing and hostel stays, but I'm strongly considering WWOOFing. I've also looked into airbnb for host reservations. Another thing I was considering is just camping around. Does anyone know how much it costs to camp, or the requirements for securing a camp site?

Phone/Internet

I was going to purchase a pocketwifi for around $130/month from http://www.globaladvancedcomm.com/pocketwifi.html. Is there a cheaper way to go about this?

Itinerary

I want to do a quick trip to see Tokyo, Osaka and Hiroshima, but I'm feeling a strong pull to Hokkaido for whatever reason and I'm thinking of spending ~2-3 weeks there. Does anyone know the transportation situation in Hokkaido? Is it easy to get around? Is it cost efficient?

Weather

I know I'll be in Japan during rainy weather, so what's the best way to be prepared? Can I just wear comfortable sandals through the rain, or will it be too cold? If I'm trying to pack light any recommendations on things to pack to be prepared?

I know this was a fat post, but I appreciate anyone who takes the time to read it and give me some feedback.